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A study of ASP 30 steel surface modification with high intensity Ti:sapphire laser, operating at 804 nm wavelength and pulse duration of 60 fs, in vacuum ambient, is presented. ASP 30 steel surface variations were studied at laser intensities of 1014 and 1013 W/cm2. The steel target specific surface changes and phenomena observed are: (i) Creation of craters at 1014 W/cm2 intensity; (ii) formation of periodic surface structures only at the reduced intensity of 1013 W/cm2; (iii) chemical surface changes registered only at higher laser intensity, and (iv) occurrence of plasma in front of the surface, including its emission in X-ray region. It can be concluded from this study that the reported laser intensities can effectively be applied for ASP 30 steel surface modification. Careful choosing of laser intensity and pulse count can lead to precise superficial material removal, for example laser intensity ~1013 W/cm2 and low pulse count can lead to ultra-precise surface processing. Generally, femtosecond laser surface modification of ASP 30 steel is non-contact and very rapid compared with traditional modification methods.
A double layer a-CN/TiAlN coating deposited on ASP30 steel substrate was irradiated by femtosecond laser and surface modification effects were observed. Moderate laser intensities used were in the range of 1014–1013 W/cm2, while the total thickness of double layer coating was 4.8 µm (a-CN = 0.6 and TiAlN = 4.2 µm). Laser-induced changes of the surface showed dependence on laser intensity and number of accumulated pulses. Irradiations at the highest intensity resulted in preservation of one or both layers up to 10 pulses, while at lower intensity (1013 W/cm2) a-CN layer is removed after several pulses and TiAlN is preserved up to 50 pulses. Evaluated damage threshold of the target was 0.49 J/cm2. Lower laser intensity irradiation produced periodic surface structures (LIPSS) over the entire irradiated spot with periodicity of ~700 nm, almost in agreement with the laser wavelength used. Irradiations carried out at the highest laser intensity (1014 W/cm2) and laser pulse count of ≥50 resulted in the creation of crater like damages with depth up to 20 µm. Craters were conically shaped, implying intensive processes which took place at the surface. Generation of LIPSS as well as craters can be of great interest for contemporary technologies.
The response of titanium surface irradiated with high intensity (1013 – 1015 W/cm2) Ti:sapphire laser was studied in vacuum. Most of the reported investigations were conducted with nano- to femtosecond lasers in gas atmospheres while the studies of titanium surface interacting with femtosecond laser in vacuum are scarce. The laser employed in our experiment was operating at 800 nm wavelength and pulse duration of 60 fs in single pulse regime. The observed surface changes and phenomena are (1) creation of craters, (2) formation of periodic surface structures at the reduced intensity, and (3) occurrence of plasma in front the target. Since microstructuring of titanium is very interesting in many areas (industry, medicine), it can be concluded from this study that the reported laser intensities can effectively be applied for micromachining of the titanium surface (increasing the roughness, formation of parallel periodic surface structures etc.).
A comparative study of superficial changes on the superalloy Inconel 600, induced by a picosecond Nd:YAG laser operating at 1064, 532, and 266 nm, is presented. All of the laser wavelengths, as well as the used fluences of 2.5 (1064 nm), 4.3 (532 nm), and 0.6 J/cm2 (266 nm) were found to be adequate for inducing surface variations. Quite different surface features were produced depending on the laser wavelength used. The measured surface damage thresholds were 0.25, 0.13 and 0.10 J/cm2 for 1064, 532, and 266 nm, respectively. Drastic differences, in function of the wavelength used, were recorded for the crater depths, as well the appearance of hydrodynamic effects and periodic surface structures. Differences in crater depths were explained via an easier propagation of the first harmonic laser radiation (1064 nm) through the ejected material and plasma compared to a radiation at 532 and 266 nm. Finally, changes in the surface oxygen content caused by ultrashort laser pulses were considered.
The interaction of Ti:sapphire laser, operating at high repetition rate of 75 MHz, with nickel-based super-alloy Inconel 600 was studied. The laser was emitting at 800 nm and ultrashort pulse duration was 160 fs. Nickel-based super-alloy surface modification was studied in a low laser energy/fluence regime of maximum 20 nJ–15 mJ/cm2, for short (10 s) and long irradiation times (range of minutes). Surface damage threshold of this material was estimated to be 1.46 nJ, i.e., 0.001 J/cm2 in air. The radiation absorbed from Ti:sapphire laser beam under these conditions generates at the surface a series of effects, such as direct material vaporization, plasma creation, formation of nano-structures and their larger aggregates, damage accumulation, etc. Laser induced surface morphological changes observed on Inconel 600 were: (1) intensive removal of surface material with crater like features; (2) material deposition at near and farther periphery and creation of nano-aggregates/nano-structures; (3) sporadic micro-cracking of the inner and outer damage area. Generally, features created on nickel-based super-alloy surface by high repetition rate femtosecond pulses are characterized by low inner/outer damage diameter of less than 11 µm/30 µm and relatively large depth on the order of 150 µm, in both low (10 s) and high (minutes) irradiation time regimes.
In this work, the interaction of a transversely excited
atmospheric (TEA) CO2 laser with tungsten–titanium
(W-Ti) alloy deposited on austenitic stainless steel is considered.
The W-Ti alloy as a refractory material possesses very good
physicochemical characteristics such as thermochemical stability
and high melting temperature. Studying of interactions of different
energetic particles or laser beams with W-Ti coatings has both
application and fundamental importance.
The morphological features of the W-Ti coating, deposited on
austenitic stainless steel AISI 316, induced by a TEA
CO2 laser after multipulse cumulative laser action,
have been considered. The laser pulses with tail (FWHM = 120
ns, tail = 2 μs) and free-tail pulses (FWHM = 80 ns) have
been employed. Laser pulses used in the experiment had equal
peak power density I = 120 MWcm−2.
For the given peak power density, excessive surface changes
on the coating were registered. From direct observation on a
microscopic scale (OM, SEM), it can be concluded that W-Ti coatings
show different behavior under laser irradiation with various
temporal pulse shapes.
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